I know that "lugging" is not good for any motor; especially the bigger CC motors.
I try to keep mine above 2,200rpms in every gear. As for the Top end work; all I got from the (coffee conversations) at the local restaurant hangout for retirees in town with bikes was alittle vague but some have put larger Cams and Stage 1 kits in. I have a Oil cooler on mine. One guy has put that on and a head fan on his also. Me personally, have kept mine all original and have had no problems. I only have about 8,000 miles on mine because of the bad weather we have here in Michigan lately. But as far as the 103 motors, I can say that they run very warm and are alot more easy on the legs and stuff during the cooler months of riding. I personally ride until it gets in the 40's and then for me, it's time to put her away until spring time.